Secondary electron multiplier consisting of single sawtooth multiplying surface

ABSTRACT

A secondary electron multiplier comprising a supporting plate having two kinds of inclined surfaces, one of which has a coating of low-resistance material and on which coating a secondary emissive layer is formed, the other of which has a coating of high-resistance material, the low-resistance and high-resistance coatings forming a series circuit across which a voltage source is connected so that a repeller electric field which serves to accelerate secondary electrons is built up around the surfaces of said secondary emissive layers.

United States Patent Inventor Haruo Maeda Osaka, Japan Appl. No. 828,277 Filed May 27, 1969 Patented Nov. 16, 1971 Assignee Matsushita Electric Industrial Co. Ltd.

O k J p Priority May 31, 1968 Japan 43/37665 SECONDARY ELECTRON MULTIPLIER CONSISTING OF SINGLE SAWTOOTH MULTIPLYING SURFACE 5 claims, 4 Drawing Figs.

05. Cl 313/ 105, 328/243 Int. Cl ..l-l0lj 43/04, l-10lj 43/18, l-lOlj 43/20 FieldotSearch 313/103, 104, 105

[56] References Cited UNITED STATES PATENTS 3,197,662 7/1965 Schneeberger 313/104 3,244,922 4/1966 Wolfgang 313/103 X 3,349,273 10/1967 Gregg 313/105 X Primary Examiner- Robert Segal Attorney-Stevens, Davis, Miller & Moshe-r ABSTRACT: A secondary electron multiplier comprising a supporting plate having two kinds of inclined surfaces, one of which has a coating of low-resistance material and on which coating a secondary emissive layer is formed, the other of which has a coating of high-resistance material, the low-resistance and high-resistance coatings forming a series circuit across which a voltage source is connected so that a repeller electric field which serves to accelerate secondary electrons is built up around the surfaces of said secondary emissive layers.

PATENTEDNBV 16 I97! sum 1 hr 2 PRIOR ART Mama finial? INVENTOR BY fi'VEMI AN/S,

My lay/h7 4 ATT BINEYS SECONDARY ELECTRON MULTIPLIER CONSISTING F SINGLE SAWTOOTI-I MULTIPILYING SURFACE This invention relates to improvements in channel-type secondary electron multiplier.

It is an object of this invention to provide an improved secondary electron multiplier having an increased multiplication factor.

It is another object of this invention to provide an improved secondary electron multiplier having a supporting plate which has two kinds of inclined surfaces, one for depositing thereon a secondary emissive material and the other for depositing a highly resistive material.

These and other objects will be effected by this invention as will be apparent from the following description taken in accordance with the accompanying drawings, throughout which like references indicate like parts in which:

FIG. 1 is a schematic view of a conventional secondary electron multiplier of channel type.

FIG. 2 is an explanatory view of the electrons emitted in the secondary electron multiplier of FIG. 1.

FIG. 3 is a schematic view of a secondary electron multiplier of this invention.

FIG. 4 is an explanatory view of the electrons emitted in the secondary electron multiplier of FIG. 3.

Referring to FIG. 1, a conventional channel-type secondary electron multiplier generally comprises parallel disposed plates 11 and 12 which are coated on their interior surfaces with secondary emissive material to form secondary emissive layers 13 and 14, respectively. These layers 13 and 14 have external terminals 15, 16, 17 and 18 at their ends, of which the terminals and 17 are connected to the negative tenninal of a voltage source 19 and the terminals 16 and 18 to the positive terminal of the voltage source 19. Thus, equipotential planes are built up normal to the secondary emissive layers 13 and 14, as indicated by the dotted lines of FIG. 2. Normal to these equipotential planes an electric field is established between the plates 11 and 12, which electric field serves to accelerate secondary electrons emitted from the secondary emissive layers 13 and 14 in the axial direction. The operation of the secondary electron multiplier is as follows: primary electrons 20 (FIG. 2) supplied from a source of primary electrons (not shown) are caused to impinge on the secondary emissive layer 14 near the external terminal 17, releasing a greater number of secondary electrons than that of the incident primary electrons. The released electrons trace parabolic trajectories, as generally indicated at 21, under the influence of the axial electric field, impinging on the surface of opposite secondary emissive layer 13. Upon impingement of the secondary electrons on the secondary emissive layer 13, a greater number of another secondary electrons than that of the secondary electrons are liberated from the layer 13, tracing similar parabolic trajectories 22 to strike on the secondary emissive layer 14. This process repeats until multiplied secondary electrons are captured by a collector electrode 23 positioned in the neighborhood of the output end of the secondary electron multiplier it). In the secondary electron multiplier of this type, the frequency at which electrons are caused to impinge on the secondary emissive layers l3 and 114 and accordingly the factor by which electrons are multiplied is proportional to the length of the secondary emissive layers 13 and I4 and is inversely proportional to the gap therebetween. Thus, in order to have available an increased multiplication factor, it is necessary that the secondary emissive layers 13 and 14 be rendered longer and the gap therebetween smaller. Furthermore, equipotential planes normal to the electric field established between the two secondary emissive layers 13 and 14 should be uniformly normal to the secondary emissive layers. However, the increase in the length of the secondary emissive layers would only impair the compactness of the secondary electron multiplier.

Such a difficulty is eliminated in the secondary electron multiplier of this invention. Referring in detail to FIG. 3, a secondary electron multiplier 24 of the invention largely comprises a secondary electron emitting plate 25. The secondary electron emitting plate 25 comprises a supporting member 26 of generally sawtooth section having two kinds of inclined surfaces 27 and 28. The supporting member 26 has on each of the long inclined surfaces 27 a coating 29 of low-resistance material such as metal, and on the surface of the coating 29 there is formed a secondary emissive layer 30. The secondary emissive layer 30 may be of any suitable material such as magnesium oxide or potassium chloride which has a high ratio of secondary emission and a high resistance. The supporting member 26 may be made of glass or ceramic. On each of thei short inclined surfaces 28 of the supporting member 26 of a, coating 31 of highly resistive material :is deposited. And these low-resistive coatings 29 and high-resistance coatings 31 are electrically connected in series with each other.

In FIG. 4, the resistances 32 represent resistances given by the highly resistive layer 31.

External terminals 33 and 34 are connected to the seriesconnected low-resistance and high-resistance coatings 29 and 31 at the opposite ends thereof for applying thereto an accelerating voltage. A voltage source 35 is connected across the external terminals 33 and 34. Since each of the secondary emissive layers 30 forms a substantially equipotential plane due to the presence of the low-resistance coatings 29 underlying the secondary emissive layers 30, equipotential planes are built up as indicated by the dotted lines 36 (FIG. 4).

An electrode 37 for collecting multiplied secondary electrons is positioned near the output end of the secondary electron emitting plate 25. Between the electrode 37 and the extema] terminal 34 is connected a voltage source 38 for maintaining the electrode 37 at a positive potential with respect to the external terminal 34, so that the secondary electrons leaving the secondary electron emitting plate 25 may be substantially totally captured by the electrode 37.

In the operation of the electron and multiplier shown in FIG. 3, electrons 39 from a source of primary electrons (not shown) are caused to impinge upon the secondary emissive layer 30 nearest to the external terminal 33 by suitable means, releasing a greater number of secondary electrons than that of the incident primary electrons 39. These emitted secondary electrons trace parabolic trajectories as: generally indicated at 40 under the influence of the electric field normal to the equipotential planes 36 and impinge upon the following secondary emissive layer 41, liberating other secondary electrons which are then caused to impinge upon the next secondary emissive layer 42. This process repeats until the secondary emissive layer nearest to the external terminal 34 is excited by the secondary electrons emitted from the preceding secondary emissive layer to release secondary electrons which are captured by a collector electrode 37.

In this embodiment, it is important that the secondary electron emitting plate 25 be of such a configuration as to give the highest possible ratio of secondary emission. It should be noted that a higher multiplication factor than those obtained with the conventional channel-type electron multiplier can be attained since, as best understood from. the inspection of the equipotential planes 36 near the secondary emissive layers 30, 41 and 42, the layers face the incident electrons approximately normally thereto.

The layers 29, 30 and 31 can be applied to the supporting member 26 firstly by evaporating a low-resistance material such as metal and secondly by a secondary emissive material on each of the long inclined surfaces 27 from one side. A highly resistive material is then applied to each of the short inclined surfaces 23 from the other side.

What is claimed is:

ll. An electron multiplier consisting of a single sawtooth multiplying surface comprising:

a. a source of primary electrons;

b. an insulating supporting plate having first and second kinds of inclined flat surfaces alternately and regularly positioned along its length, said plate having an upper surface portion shaped in a sawtooth form;

c. a low-resistance material coating on said first kind of inclined surface;

d. a secondary emissive layer on and in electrical contact with said low-resistance material coating;

e. a high-resistance material coating on said second kind of inclined surface, said low-resistance and high-resistance coating being connected to each other forming a series circuit to yield secondary electron multiplication, the inclined surfaces for depositing said secondary emissive layer being longer than the inclined surfaces for depositing said highresistance coating;

f. a voltage source connected across said series circuit to establish electron-accelerating electric fields around the surfaces of said secondary emissive layers, the secondary electrons emitted from the respective emissive surfaces due to incoming primary electrons accelerating toward and impinging upon the following emissive surfaces at a 4 high potential; and g. a collector electrode kept at a positive potential with respect to said secondary emissive layers. 2. An electron multiplier as set forth in claim 1, in which said secondary emissive layer is composed of magnesium oxide.

3. An electron multiplier as set forth in claim 1, in which said secondary emissive layer is composed of potassium chloride.

4. An electron multiplier as set forth in claim 1, in which said supporting plate is composed of glass.

5. An electron multiplier as set forth in claim 1, in which said supporting plate is composed of ceramic. 

1. An electron multiplier consisting of a single sawtooth multiplying surface comprising: a. a source of primary electrons; b. an insulating supporting plate having first and second kinds of inclined flat surfaces alternately and regularly positioned along its length, said plate having an upper surface portion shaped in a sawtooth form; c. a low-resistance material coating on said first kind of inclined surface; d. a secondary emissive layer on and in electrical contact with said low-resistance material coating; e. a high-resistance material coating on said second kind of inclined surface, said low-resistance and high-resistance coating being connected to each other forming a series circuit to yield secondary electron multiplication, the inclined surfaces for depositing said secondary emissive layer being longer than the inclined surfaces for depositing said highresistance coating; f. a voltage source connected across said series circuit to establish electron-accelerating electric fields around the surfaces of said secondary emissive layers, the secondary electrons emitted from the respective emissive surfaces due to incoming primary electrons accelerating toward and impinging upon the following emissive surfaces at a high potential; and g. a collector electrode kept at a positive potential with respect to said secondary emissive layers.
 2. An electron multiplier as set forth in claim 1, in which said secondary emissive layer is composed of magnesium oxide.
 3. An electron multiplier as set forth in claim 1, in which said secondary emissive layer is composed of potassium chloride.
 4. An electron multiplier as set forth in claim 1, in which said supporting plate is composed of glass.
 5. An electron multiplier as set forth in claim 1, in which said supporting plate is composed of ceramic. 